Vehicle steering system for controlling a steering or steering lock angle of at least one wheel of a vehicle

ABSTRACT

The invention relates to a vehicle steering system for controlling a steering or steering lock angle of at least one wheel of a vehicle, comprising the following: a steering handle, especially a steering handwheel; a detecting device for detecting the degree of actuation of the steering handle; a mechanical interconnection between the steering handle and the at least one steered vehicle wheel; an adjustment unit for assisted adjustment of the steering or steering lock angle; a control device for the adjustment unit, wherein the actual manual torque or force that is to be exerted by the driver to control the vehicle is regulated by the control device depending on vehicle state parameters, wherein the control device has a vehicle state regulator which generates an adjustment parameter T req  with the aid of state parameters of the vehicle, in which the steering forces exerted by the driver would be minimal, so that practically torque-free steering could be realized and a reference variable lock-on produces a reference variable T ref  for the manual torque T driver, req  to be exerted by the driver.

[0001] The present invention relates to a vehicle steering system for controlling a steering or steering lock angle of at least one wheel of a vehicle with the features of the preamble to claim 1.

[0002] With hydraulic power-assisted steering systems, as a rule a control valve controls an oil pressure in the steering cylinder in a manner corresponding to the rotary movement of the steering wheel. An elastic torque-measuring element, such as a torsion bar, helical spring, or leaf spring, converts the torque engaging at the steering wheel into a control travel movement. By means of the control travel, control edges designed as bevelled or chamfered elements or facets are displaced, and so form the corresponding aperture cross-section for the oil flow.

[0003] With power-assisted steering systems in which the supporting torque is created by means of an electric motor as an actuator, a torque-measuring device likewise serves as a rule for measuring the manual torque applied by the driver.

[0004] Increasing demands with regard to the operating convenience of power-assisted steering and the safety of the vehicle have led to the introduction of parameterable power-assisted steering systems. These work, for example, as a function of the speed; i.e. the travel speed displayed by the electronic tachometer controls or influences the actuation force to be applied to the steering wheel or the steering handle by the driver. A control device assesses the speed signals and determines the value of the supporting torque to be adjusted, which is required by the actuator to provide the supportive setting of the steering or steering lock angle. In this way, the special design of the steering characteristics can lead to the situation in which, when carrying out parking maneuvers and when turning the steering wheel while stationary, only minimal force is to be applied to the steering wheel, while with increasing speed of the vehicle the amount of the assistance force and assistance torque is reduced. Accordingly, at high speeds exact and precisely-aimed steering is made possible.

[0005] A disadvantage of the known power-assisted steering systems is the fact that the manual torque applied to the steering handle or steering wheel is measured and only passed on to the actuator device with amplification. As a result of this, only an inadequate degree of operating comfort and convenience is attained. With these systems, as a rule, the active return, i.e. the return of the released steering wheel to the central setting, is implemented explicitly by means of an additional control device, as a result of which the entire regulation/control of the system is complicated and prone to failure. The implementation of active damping or attenuation can only be achieved in the conventional systems with substantial effort and in most cases is unsatisfactory. In addition, a disadvantage of these systems that friction compensation, i.e. the taking into consideration of the friction present in the steering system, may not be considered, or only insufficiently. By the implementation of the options referred to above, the controller is in most cases so complex that it can only be optimized with great effort, if at all.

[0006] The object of the present invention is to provide a vehicle steering system which is easier to optimize, in which the manual torque to be applied by the driver can be predetermined and, in particular, can be precisely adjusted.

[0007] This problem is resolved according to the invention by a generic vehicle steering system with the features of claim 1. Other embodiments of this vehicle steering system according to the invention are derived from the features of the sub-claims.

[0008] The essential thinking behind the invention is that a state or condition regulator creates a setting value T_(req) for the control device by means of state values from the vehicle, in which the steering forces to be applied by the driver would be minimal, with the result that a steering system would be created which would as far as possible be torque-free. Taking torque-free steering as a starting point, a guide value T_(ref) can be easily totaled up from the setting value T_(req), without any consideration needing to be paid, during the calculation or determination of the manual torque to be applied by the driver, to the vehicle state values which are otherwise to be considered. As a result it is possible advantageously for the torque applied by the driver to be actively predetermined and not, as with the prior art, only the manual torque actually measured being taken for the calculation of the degree of amplification required to support the driver. An alternative solution to engaging a guide value is derived if the setting value T_(req) is multiplied by a proportionality factor, which in turn is dependent on various different values such as the travel speed and the sensor torque moment.

[0009] Thus, for example, the manual torque to be applied by the driver, T_(driver,req), can be a function of the following parameters: Steering wheel angle, vehicle speed, interference forces acting on the vehicle steering, such as tie rod forces and forces on the tires or reaction forces between the tires and the carriageway, various dynamic travel information from the travel systems located in the vehicle, in particular the transmission and/or the travel dynamics regulation system.

[0010] It is self-evident that the function referred to above does not have to take account of all the parameters listed. All these parameters can be considered individually or in different combinations. It is likewise possible advantageously for the vehicle driver to specify for the steering in advance that he wishes to drive in a sporty, comfortable, or energy-saving manner. By means of such advance instructions, the actively specified manual torque required, T_(driver,req), can be calculated differently for the individual driving situations and precisely predetermined.

[0011] It is, however, advantageous if at least some of the parameters indicated are taken into account for the function of the manual torque to be applied.

[0012] The actively specified manual torque required, T_(driver,req), can also be calculated by the multiplication of T_(friction) by a proportionality factor k_(assist), which can, for example, be the vehicle speed values v_(vehicle) and the sensor torque T_(sensor).

[0013] Advantageously the control device of the steering system according to the invention is provided with an observation element, which, by means of a mathematical model of the steering system of the vehicle, calculates the state values of the vehicle which are not measured and/or cannot be measured. Such simulation models exist for every vehicle, with the result that advantageously unnecessary sensors for the determination of road condition values and interference state values can be done away with.

[0014] The term road condition values is understood to mean, inter alia, the pinion-side angle velocity Ω_(pinion), the angle difference between the steering wheel side and pinion side Δφ, the angle velocity difference between the steering wheel side and pinion side ΔΩ, and the torque T_(motor) derived from the actuator. It is self-evident that equivalent values can likewise be taken into consideration for the steering system according to the invention.

[0015] The term interference state values is understood to mean, inter alia, the torque T_(driver) applied by the driver, as well as the friction moments engaging on the steering system T_(friction).

[0016] To achieve torque-free steering behavior, the state regulators require the road state values and interference state values of the road, i.e. of the steering system, for the feedback or engaging procedures.

[0017] Road state values in the sense of the state space theory are, for example: ${\underset{\_}{x}}_{p} = \begin{bmatrix} \Omega_{pinion} \\ {\Delta \quad \phi} \\ {\Delta \quad \Omega} \\ T_{motor} \end{bmatrix}$

[0018] where

[0019] Ω_(pinion) is the pinion-side angle velocity,

[0020] Δφ is the angle difference between the steering wheel side and the pinion side,

[0021] ΔΩ is the angle velocity difference between the steering wheel side and the pinion side,

[0022] T_(motor) is the torque emitted by the actuator.

[0023] The following can be regarded as interference state values, for example: ${\underset{\_}{x}}_{d} = \begin{bmatrix} T_{driver} \\ T_{friction} \end{bmatrix}$

[0024] where

[0025] T_(driver) is the torque applied by the driver

[0026] T_(friction) is the friction moment engaged at the steering system.

[0027] Due to the feedback of the road state values by means of a suitable matrix Kp and the lock-on of the interference states (friction value or interference value compensation) via a suitable matrix Kd, which are calculated by means of a suitable state regulator design with a road model extended by an interference model, provision is made for the selected target values, e.g. ${\underset{\_}{y}}_{po} = \begin{bmatrix} T_{sensor} \\ {\Delta \quad \Omega} \\ {\Delta\alpha} \end{bmatrix}$

[0028] to be regulated out to zero by the actuating signal T_(req) produced by the controller. These target values are freely selectable, but must be dependent on the road states. In the equation above, the target value T_(sensor) for the realization of torque-free control, the target values ΔΩ and Δα serve to achieve active oscillation damping, which accordingly allows “torque-free” steering to be achieved.

[0029] A number of basic interconnections of the invention are explained in greater detail hereinafter, on the basis of drawings.

[0030] These show:

[0031]FIG. 1: A diagrammatic representation of the realization of a torque-free vehicle steering system;

[0032]FIG. 2: A guide value lock-on arrangement according to the invention;

[0033]FIG. 3: A state observation element according to the invention;

[0034]FIG. 4: Function blocks of the control concept according to the invention;

[0035]FIG. 5: An alternative solution for the generation of the desired driver torque T_(driver,req);

[0036]FIG. 6: An alternative solution for the guide value lock-on according to FIGS. 3 and 5.

[0037]FIG. 1 shows a diagrammatic representation of the realization of a torque-free vehicle steering system by state vector feedback with interference value compensation.

[0038] Once torque-free steering has been achieved, a desired steering sensitivity can be obtained by means of a guide value model. The term steering sensitivity in this context is understood to mean the manual torque felt by the driver or to be applied by the driver. To do this, the value T_(ref) is generated from the manual torque T_(driver,req) to be felt by the driver by means of a guide value lock-on with matrix Kr, and totaled to form the adjustment parameter T_(req).

[0039]FIG. 2 shows the guide value lock-on and the summation of the values T_(req) and T_(ref) to T_(req), whereby T_(req) is an adjustment parameter for the control device of the actuator.

[0040] The target values to be weighted therefore become: ${\underset{\_}{y}}_{w} = \begin{bmatrix} {T_{sensor} - T_{{driver},{req}}} \\ {\Delta \quad \Omega} \\ {\Delta\alpha} \end{bmatrix}$

[0041] T_(driver,req) is the torque which the driver feels. In comparison with the target value vector Y_(po), no torque-free steering (i.e. T_(sensor)=0) is produced here, but a reduced sensor moment is controlled around the amount of the desired driver torque T_(driver,req). Due to the previously engendered torque-free steering behavior, the drive sensitivity, i.e. the torque value T_(driver,req), is now a completely freely formable value (independent of the road states), and can be any desired function of the parameters already described.

[0042] Because it is not normally possible for all the required state values to be measured, they must be reconstructed from the existing measured values. This can be done, for example, by a differentiating filter or the state observation element already described.

[0043] As FIG. 3 shows, the state observation element can exhibit a mathematical parallel model of the road, extended by an interference model, and receives as input values the adjustment parameter T_(req) generated by the controller, as well as the measured values which are in fact present, such as the torque T_(sensor) and the engine angle φ_(motor).

[0044] By means of the feedback of the differences from the calculated measured values and the actual measured values via a suitable matrix, the missing state values can be determined. The calculation of this matrix can be determined by means of a suitable observation arrangement.

[0045] By interconnecting the observation element and the controller, a control arrangement can be derived for friction compensation, freely adjustable driver sensitivity and active oscillation damping.

[0046]FIG. 4 shows functional blocks of the control concept according to the invention for the vehicle steering system. The observation element determines the input values required for the controller. By simultaneous guide value lock-on of T_(driver,req), the controlling system controls the adjustment parameter T_(req) in accordance with the manual sensitivity or manual torque which is to be set.

[0047] As has already been explained, T_(req) is the adjustment parameter for the control device of the actuator. Thanks to the advantageous modular arrangement of the vehicle steering system according to the invention and its control concept, it is possible to implement the concept according to the invention in any vehicle without problem. The control layout in this situation is very simple in design, since as a rule the mathematical models for the individual vehicles are known.

[0048] As a result of the fact that a torque-free steering system is put into effect first, it is possible without any problem for a function developed for a particular vehicle for the drive sensitivity or manual torque to be applied by the driver to be adopted for another vehicle. It is therefore possible for different vehicles to be equipped with exactly the same drive sensitivity.

[0049] The control concept represented in the drawings is only one possible embodiment of the vehicle steering system according to the invention. It is of course possible for the summation of T_(ref) and T_(req) to be effected at another point. For example, the individual matrices Kr, Kp, and Ka can naturally be combined into one single matrix without departing from the concept according to the invention.

[0050]FIG. 5 shows an alternative means of generating the desired driver torque T_(driver,req), whereby the desired driver torque T_(driver,req) is derived by the multiplication of T_(friction) by a proportionality factor k_(assist). The factor k_(assist) is in turn a function of different values such as, for example, the vehicle speed v_(vehicle) and the sensor torque T_(sensor).

[0051] As an alternative to the guide value lock-on, it is likewise in the sense of the invention if the value T_(req) is multiplied by a proportionality factor. This proportionality factor can be k_(assist), as shown in FIG. 6. 

1. Vehicle steering system for controlling a steering or steering lock angle of at least one wheel of a vehicle, which has: A steering handle, in particular a steering wheel; A detection device for recording the degree of actuation of the steering handle; A mechanical actuation link between the steering handle and at least one steered vehicle wheel; An actuator to provide supported adjustment of the steering or steering lock angle; A control device for the actuator, whereby the actual manual torque or force to be applied by the driver to control the vehicle is regulated by the control device as a function of the vehicle state values; characterized in that the control device has a state regulator, which generates an adjustment parameter T_(req) for the control device by means of state values of the vehicle, in which the steering forces to be applied by the driver would be minimal, so that the most torque-free possible steering would be achievable, and that a reference value lock-on for the manual torque T_(driver,req) to be applied by the driver produces a guide value T_(ref).
 2. Vehicle steering system according to claim 1, characterized in that the multiplication of the value T_(friction), which represents the friction moments engaging on the steering, with a variable proportionality factor k_(assist), produces the manual torque to be applied by the driver, T_(driver,req).
 3. Vehicle steering system for controlling a steering or steering lock angle of at least one wheel of a vehicle, which has: A steering handle, in particular a steering wheel; A detection device for recording the degree of actuation of the steering handle; A mechanical actuation link between the steering handle and at least one steered vehicle wheel; An actuator to provide supported adjustment of the steering or steering lock angle; A control device for the actuator, whereby the actual manual torque or force to be applied by the driver to control the vehicle is regulated by the control device as a function of the vehicle state values; characterized in that the control device has a state regulator, which generates an adjustment parameter T_(req) for the control device by means of state values of the vehicle, in which the steering forces to be applied by the driver would be minimal, so that the most torque-free possible steering would be achievable, and in that the guide value T_(ref) is generated by multiplying the adjustment parameter T_(req) by a proportionality factor k_(assist).
 4. Vehicle steering system according to claim 3, characterized in that the proportionality factor k_(assist) is a function of the vehicle speed and the sensor torque T_(sensor).
 5. Vehicle steering system according to one of the foregoing claims, characterized in that the control device has an observation element, which by means of a mathematical model of the steering system of the vehicle, determines state values of the vehicle which are not measured and/or cannot be measured.
 6. Vehicle steering system according to one of the foregoing claims, characterized in that, for the calculation of T_(req), road state values and interference state values are taken into consideration.
 7. Vehicle steering system according to claim 6, characterized in that the road state values are, for example, the pinion-side angle velocity Ω_(pinion) and/or the angle difference between the steering wheel side and the pinion side Δφ and/or the angle velocity difference between the steering wheel side and the pinion side ΔΩ and/or the torque T_(motor) issued by the actuator, and/or equivalent values.
 8. Vehicle steering system according to claim 6, characterized in that interference state values are the torque T_(driver) applied by the driver and/or the friction torque T_(friction) engaging on the steering system.
 9. Vehicle steering system according to one of claims 6 to 8, characterized in that, by feedback of the road state values by means of a suitable matrix Kp and lock-on of the interference state values by means of a suitable matrix Kd, the adjustment parameter T_(req) is generated.
 10. Vehicle steering system according to one of the foregoing claims, characterized in that, by means of a guide value lock-on in a matrix Kr, a desired manual torque T_(driver,req) is added up to the adjustment parameter T_(req).
 11. Vehicle steering system according to claim 10, characterized in that the desired manual torque T_(driver,req) is a function of the steering wheel angle and/or the vehicle speed and/or the interference values acting on the vehicle steering system, such as tie rod forces and/or forces on the tires and/or reaction forces between tires and carriageway.
 12. Vehicle steering system according to claim 10 or 11, characterized in that the desired manual torque T_(driver,req) can be specified by input by the vehicle driver and/or can be influenced thereby.
 13. Vehicle steering system according to claim 12, characterized in that an input for the setting of the driving mode is, for example, “economy” or “sport”.
 14. Vehicle steering system according to one of claims 10 to 13, characterized in that the desired manual torque T_(driver,req) is a function of various different items of driving dynamic information from the various driving systems located in the vehicle, in particular from the transmission and/or the vehicle dynamics control system.
 15. Vehicle steering system according to one of the foregoing claims, characterized in that state values of the vehicle which are not measured are determined by differentiating filters or notified to the observation element.
 16. Vehicle steering system according to one of the foregoing claims, characterized in that the state regulator is arranged by means of a quality function element in such a way that an active vibration damping effect is achieved. 